1. Field of the Invention
The present invention relates to a process for producing a phenolic chelate resin having a selective adsorbability to a heavy metal using a phenol, an aldehyde, and iminodiacetic aicd. The invention is further relates to a simple process for producing a phenolic chelate resin having excellent heavy metal chelating ability and capable of being reused.
2. Description of the Prior Art
For a long time various investigations have been made on phenolic chelate resins prepared by introducing chelating group into a phenol nucleus. However, since the chelating group is chemically unstable, the cost of raw materials is high, and also the production cost becomes high. As a result very few chelate resins are commercially available and further the commercially available chelate resins are also restricted in their reuse due to the unstability of the chelating group.
Materials such as iminodiacetic acid which are capable of forming chelate compounds by coordination with heavy metal ions are well known and research on metal chelation has now been extended to various fields such as organic reagents for inorganic analytical chemistry, chelate titration, solvent extraction of metal ions, complex salt dyes, chelate pigments, and blocking agents for metal ions for use in the chemical industry. On the other hand, chelate resins prepared by introducing into high molecular weight compounds ligands which are capable of forming chelate compounds with heavy metal ions, that is, compounds having chelating groups so that they can coordinate with heavy metals due to chelation have been reported in various publications.
However, the kinds of commercially available chelate resins are very few since the chelating groups introduced into high molecular weight materials are generally poor in chemical stability as compared with ordinary ion-exchange groups such as a sunfonic group, a carboxyl group, and a quaternary ammonium group. This makes the reuse of such chelate resins difficult, the cost of the chelating group itself is high, and the procedure of introducing the chelating groups into high molecular weight materials is comparatively complicated, which results in greatly increasing the cost of the chelate resins as compared with ordinary ion-exchange resins.